Why PPAP is rejected by OEMs and Tier 1? The most common causes and practical ways to prevent them

PPAP as a supplier maturity test – metal stamping and beyond

In the OEM and Tier 1 environment, PPAP in projects involving metal stamping is not a formality. It is a tool whose primary purpose is to confirm that the production process is stable, repeatable, and fully compliant with customer requirements—before serial production begins.

In practice, many PPAP rejections do not result from “documentation errors,” but from a lack of consistency between the documentation and the actual process (such as metal stamping), unclear customer expectations, or insufficient risk analysis during the project preparation phase.

From Mikrostyk’s perspective, operating as a Tier 2 supplier to Tier 1 customers, PPAP is part of a broader quality management system rather than a one-off “package to be submitted.”

 

 

PPAP according to AIAG vs. the OEM / Tier 1 reality

The AIAG PPAP manual provides a solid foundation, but in real-life projects almost every OEM and Tier 1 customer applies its own customer specific requirements (CSR). These typically include:

  • dedicated PPAP checklists, 
  • customer portal requirements, 
  • additional tests (e.g. cleanliness), 
  • detailed guidelines for packaging and traceability,
  • individual expectations regarding capability or MSA.

A mature supplier—not limited to metal stamping—treats PPAP not as mere “compliance with AIAG,” but as a response to the customer’s specific risks and expectations.

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The most common causes of PPAP rejections – a market perspective

Based on observations from projects carried out for OEMs and Tier 1 customers (without referring to Mikrostyk’s own experience), three critical areas recur most frequently.

1. Incomplete or ambiguous understanding of customer requirements
In practice, this leads to:

  • missing required PPAP elements, 
  • incorrect document formats,
  • missing signatures, dates, or revision levels.

2. Capability below customer expectations
A typical scenario looks as follows:

  • the process formally operates (metal stamping, cutting, or any other),
  • parts meet dimensional requirements,
  • however, Cp / Cpk < 1.33 for significant characteristics.

The root cause is not always the process itself, but often:

  • too short a production run for analysis,
  • improperly selected characteristics,
  • lack of confirmed process stability over time.

For OEMs and Tier 1 customers, capability is not just a statistical value—it is proof of process control.

3. Product nonconformance with the drawing or specification
It can happen that, despite multiple attempts, not all characteristics fall within drawing tolerances, and the deviations are not clearly stated in the PSW.

This may result in an initial PPAP rejection, which in practice is often the first step toward a substantive discussion about tolerances and process capability.

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A “formally complete PPAP” in metal stamping that still fails

It is not uncommon for a PPAP to contain all the required elements and yet still trigger questions or concerns from the customer. The most common reasons include:

  • ambiguous tolerance definitions on the drawing,

  • differing interpretations of technical requirements,

  • lack of a clear link between measurement results and specific customer requirements.

This shows that PPAP is first and foremost a technical dialogue, and only secondarily a set of documents.

PFMEA and control plan – areas of special attention

From the perspective of OEMs and Tier 1 customers, a key warning signal is a lack of consistency between the PFMEA, the control plan, and the actual process flow.

The most commonly observed market issues include:

  • PFMEA not being updated after changes,
  • a control plan disconnected from production reality,
  • no clear linkage between identified risks and control methods.

In mature organizations, PFMEA is not a document prepared “for PPAP purposes,” but a living risk management tool that naturally translates into the control plan and process instructions.

Areas particularly scrutinized by OEMs and Tier 1 customers

Each customer defines its own customer specific requirements (CSR), the scope of which depends on the project, industry, and product application. Most commonly, these include:

Cleanliness

If technical cleanliness requirements are defined, customers primarily expect:

testing performed in accordance with the applicable standard and by an accredited laboratory, a consistent methodology, repeatable results and a clear link to the production process.

This is especially critical in the automotive industry, where customers rely on processes such as metal stamping.

Packaging

Requirements may relate to, among others specified packaging dimensions, the use of returnable packaging, the maximum allowable weight of a packaging unit.

Traceability
Traceability must function in practice. OEMs and Tier 1 customers expect a clear link between production batches and manufacturing, legible labeling, and consistency throughout the entire supply chain.

Process changes and PPAP – moments of increased risk

Although customers usually communicate clearly when a new PPAP is required, risk most often arises during tool modifications and changes to process parameters.

Mature organizations assess the impact of a change before the customer asks for a new PPAP—by updating the FMEA and evaluating its effect on the product.

How to reduce the risk of PPAP rejections – a system-based approach

From the perspective of an experienced Tier 2 supplier—particularly based on our background in metal stamping and metal processing—three elements are key:

1. Risk awareness, not just checklist compliance
A PPAP prepared “in accordance with AIAG” is not sufficient if it does not take customer specific requirements (CSR) and real customer expectations into account.

2. PFMEA as a foundation, not a formality
A robust risk analysis:

  • eliminates surprises, 
  • structures the control plan, 
  • shortens the approval process.

3. Process thinking instead of document thinking
OEMs and Tier 1 customers are essentially asking one question:

Does this supplier understand its process?

PPAP documentation is merely the carrier of that answer.

 
 

PPAP as an element of partnership

In mature relationships, PPAP is not an “exam,” but a confirmation of a shared understanding of the process and the product. Suppliers—not limited to metal stamping—that understand their risks, are familiar with customer specific requirements (CSR), and work with an up-to-date FMEA are rarely surprised by additional questions during the approval phase.